1. Field of the Invention
The present invention relates generally to the evaluation of the quality of bar code indicia. More particularly, the invention relates to methods and apparatus to enable the high speed collection of critical values, and other critical values, occurring within scan reflectance profile signals generated by scanning indicia, such as bar code indicia.
2. Description of the Prior Art
The scanning of bar code indicia with devices such as laser scanners, and the like, typically results in the generation of a scan reflectance profile (SRP) signal. To enable the quantitative evaluation of the quality of the scanned indicia, very often known systems (fully) digitized the SRP signal. Such systems employ an analog-to-digital converter to produce a large sequence of sample values (i.e., data), that are stored or queued in a memory device for later processing. In applications where high speed evaluation is required, the above approach, which requires the consideration (i.e., processing) of the full set of sample values, presents a limiting factor. There is a need to provide improved `higher speed` methods and apparatus to digitize and process the SRP signals generated to evaluate indicia quality.
At present, a number of industry standards or guidelines have been established to quantitatively evaluate the quality of bar code indicia. Two such guidelines have been defined by the American National Standards Institute (ANSI), and the Uniform Code Council (UCC). The ANSI guideline (ANSI X3.182-1990) is titled "Bar Code Print Quality Guideline". The UCC guideline is titled "Quality Specification for the UPC Printed Symbol" (September 1994). The ANSI and UCC documents are hereby incorporated by reference. In particular, the ANSI document provides in section 4 measurement methodologies and related information, while parts 2 and 3 of the UCC document provide definitions and related measurement subject matter. These two documents define a number of quality indicating `figures of merit` that can be determined from the sampled scan reflectance profile signal. However, since each guideline defines an entire procedure for evaluation, and further requires a succession of scans be taken at equally spaced locations within an "interrogation window" along the height of the elements forming the bar code indicia, full compliance with these standards/guidelines has presented a significant challenge when the SRP signals must be processed in what may be termed "real-time", say as indicia are being printed on retail packages or products.
As disclosed in the cross-referenced and U.S. Pat. No. 5,633,488 to Spitz, a careful review of the ANSI specification, and other like (print) quality standards, reveals that many if not all important quality parameters (or figures of merit) may be determined by considering only the level of reflectance provided by the positive peaks and the negative peaks within the SRP signal. Accordingly, the "other" non-peak sample values are of little use when considering quality parameters such as symbol contrast, modulation, edge contrast, and the like. Therefore, when considering the above prior art systems, wherein a full set of sample values are collected and stored, a "filtering" process must be carried out to first isolate the positive and negative peak values present in the full set of sample values collected. As a result, a great deal of processing time and power is consumed before the actual evaluation parameters may be determined. Further, the processing demands on a system are exacerbated where compliance is required (or desired) to provide, say, full ANSI quality reporting.
It is also known in the art to employ circuitry to produce first and second derivative signals of the scan reflectance profile signal for various purposes. These signals, which are produced as the SRP signal is generated, are generally employed to detect edges, or element boundaries, occurring within the SRP signal. The technique was developed to provide an accurate indication of the location of the element edges (or transitions) within the SRP signal, even in the presence of ambient light, noise, and the like. Those skilled in the art will recognize that peaks in the level of the first derivative signal will indicate the respective inflection points (of the SRP signal) and the occurrence of an edge therein, as will certain zero crossings of the second derivative signal. The use of the first and second derivative signals (as well as related signals produced by inverting, adding, subtracting, etc., of the derivative and SRP signals) is provided by many U.S. patents, including U.S. Pat. No. 4,000,397 to Herbert et al., and U.S. Pat. No. 5,463,211 to Arends et al. Although these and other systems have employed the first and/or second derivative signals of the SRP signal, to determine edges and transitions within the SRP signals, they have not been employed to determine peaks occurring within the SRP signal to provide for the high speed analysis of said signals, and more broadly to support the high speed evaluation of indicia, including bar code indicia.
Objects of the present invention are, therefore, to provide new and improved methods and apparatus, incorporating the use of first and or second derivative signals to analyze and selectively sample (or selectively store samples of) one or more scan reflectance profile signals to capture critical values occurring therein, having one or more of the following capabilities, features, and/or characteristics:
enable high speed analysis and evaluation scan reflectance profile signals as they are generated; PA1 process reflectance data samples as they (the samples) are generated in order to store in memory, or generally make available, only the critical (e.g., peak) sample values that are useful for various quantitative evaluations; PA1 utilizing the first and or second derivative signals to determine appropriate times to sample an SRP signal to determine (capture) the peak values, and possibly other critical values, and the corresponding level of reflectance associated with each sample determined; PA1 capture critical peak samples, along with associated and related data, which will, among other uses, support the recreation of an approximate graphical representation of one or more portions of the scan reflectance profile signal originally generated by scanning the indicia; PA1 enable the detection and quantification of indicia defects as indicia are being printed or otherwise disposed on products and packages; PA1 support real-time verification of indicia in demanding applications; PA1 significantly reduce the amount of sample memory required to store sample values collected; PA1 reduce the processing overhead (including processing time and CPU utilization) required to enable high speed ANSI level evaluation reporting; and PA1 relatively low cost implementations using many known components and devices, which are readily available.